It has been proposed to produce insulating glazing units (e.g. heat insulating double glazing units) by combining two glass panes into one unit by the use of distance-holders, spacing the panes apart at a specified distance from each other, the panes being, for example, adhesively bonded together. Great demands are made on the adhesive used, since it must bond the glass and the distance-holder sufficiently strongly together, and produce a satisfactory seal against diffusion of water-vapour. The adhesive must in addition retain these principal characteristics unchanged over a relatively wide range of temperatures, somewhere in the zone of -30.degree. C. to +40.degree. C. It is also desirable from the viewpoint of the glazing unit producer that this adhesive can be worked as a hot-melt adhesive.
Adhesives based on butyl rubber have been proposed for glazing sealants which exhibit a good sealing capacity against water-vapour diffusion and resistance to cold and heat. A large disadvantage, however, of proposed butyl-rubber based sealant adhesives resides in the fact that they are not readily processable as hot-melt adhesives. Naturally, a series of attempts has been undertaken and made known aiming at modifying butyl-rubber based compositions in such a way that they can be worked in melted condition.
Moreover, as indicated at the outset, a whole series of attempts in the modifying of butyl-rubber based compositions has been made. Thus, it has already been tried to dilute butyl-rubber compositions with relatively large quantities of asphalt or bitumen in order to impart thermoplastic properties. Such mixtures do indeed exhibit an unimpaired, good degree of proof against water-vapour diffusion and good thermoplastic behaviour, but they exhibit unsatisfactory behaviour when heated or cooled. They become very cold-brittle even within the range of hardening temperature, whilst on the other hand they quickly begin to soften when heated. Such mixtures are thus not suitable as sealing adhesive for the production of insulating glazing.
With the addition of other thermoplasts, for example by the addition of hydrocarbon polymers of the styrene type or cumaron-indene type or colophonium, colophonium-derivatives or polyethylene, butyl-rubber based compositions become more satisfactory in the desire way, but at the same time, however, the degree of proof against water-vapour diffusion is perceptibly reduced, especially with polyethylene additions with a high melt-index, and adhesion to glass and the spacer material decreases.
In German Offenlegungsschrift 2140834 a method is disclosed of using, for the production of insulating glazing units, compounds based on thermoplastic rubber block copolymers of the types Styrene/Butadiene/Styrene and Styrene/Isoprene/Styrene. The compounds are said to consist of at least 20% of one of the above-mentioned block polymers, and can contain 0 to 80%, preferably 0 to 50% of a thermoplastic polymer, which may be, among others, polyisobutylene. A disadvantage of these types of compound is that they do not adhere well enough to glass to give adequate water-impermeability. For defect-free processing, adhesive agents must be included which, within the framework of the production of insulating glazing units involves a two-stage working-process, and thereby avoidable expense. Apart from that, compositions of the kind described in Offenlegungsschrift 2140834 do not exhibit any particularly good degree of proof against water-vapour diffusion through the composition.